This project has three main goals. 1. Analysis of startle modulation. In zebrafish, startle responses are modulated in a similar fashion to mammals where startle magnitude is inhibited when the startle stimulus is preceded by a weak auditory prepulse. This form of startle modulation, termed prepulse inhibition, is diminished in several neurological conditions including schizophrenia. We previously conducted a circuit breaking screen using a brain selective enhancer trap library of Gal4 lines to ablate defined groups of neurons before testing PPI. Using this approach we determined that the transcription factor Gsx1 defines neurons required for PPI in both zebrafish and mice. We are now studying neuronal activity and connectivity of Gsx1 specified neurons. As Gsx1 neurons are broadly distributed, we are using an intersectional genetic approach to pinpoint the precise set of neurons that regulate startle thresholds. These approaches will allow us to find neuronal mechanisms for the implementation of behavioral choice in zebrafish larvae. 2. Functional mapping of neuronal architecture mediating arousal states. We previously demonstrated that water flow induces a transient state of arousal in zebrafish larvae characterized by hyperactivity and increased visual sensitivity to flow. We also demonstrated that light sensitive neurons in the preoptic area of the hypothalamus induce a state of hyperactivity in response to loss of illumination. We are continuing to characterize neuronal circuits underlying this state and have established a new paradigm for inducing a state of arousal, by activating a light-activated cation channel (channelrhodopsin) in sensory neurons. We are analyzing the different patterns of neuronal activity during these distinct states of arousal to identify components of the underlying circuits. 3. Development of new tools for analysis of neural circuits involved in motor behavior. The relatively simple nervous system of zebrafish larvae and restricted range of motor behaviors opens up the possibility of identifying neuronal pathways which underlie the entire behavioral repertoire. We previously developed transgenic tools for genetically targeting neurons in the nervous system using Gal4 lines. Using these transgenic lines, we have developed an atlas of the larval zebrafish brain and software that enables researchers to identify a transgenic line corresponding to any selected region. We are now developing computational approaches to enable automated neuroanatomical analysis of the brain. In addition, this atlas enables us to undertake systematic analysis of brain microstructure and composition in zebrafish mutants of human neurodevelopmental disorders, such as schizophrenia and autism.